The legal concept of an alibi is the plea of having been, at the time of commission of an act, elsewhere than at the place of commission of the act. Traditionally, human witnesses are relied upon to testify that a person was seen at a certain location at a given time. Reliance upon human witnesses, however, is often problematic. This is because witnesses are not always available. A witness might be considered unreliable because he or she might not have a vivid memory of the person who needs the alibi. The reliability of a witness might also be brought into question due to his or her prior relationships with that person and any resultant bias. Another reason reliance upon human witnesses is problematic is because a witness might not be willing to provide an alibi unless forced to do so by court order, especially in small personal disputes. Yet, even when there is human testimony for the presence of someone at some location, evidence independent of this testimony could strengthen an alibi.
In some cases, including those described above, it would be beneficial for people to have access to a system that can provide a location corroboration. Since people often carry a smartphone or other device with location-determining capabilities, it might be effective to use such device(s) as a tool to provide location corroborations. A location corroboration should be reliable such that a user could not fake location data. Moreover, to protect user privacy, the location of the user should not be revealed to anyone, unless necessary as part of a location proof procedure. Reliability is not a simple task because users can easily fake global positioning system (“GPS”) readings provided by smartphones. For this reason, a simple method that merely records the GPS location of a smartphone for which a location corroboration is desired is unreliable. Adding to the complexity of any location corroboration scheme is maintaining private the location of the user.